1. Field of the Invention
The embodiments of the invention provide an apparatus and method for detection and compensation of negative bias temperature instability (NBTI) induced threshold degradation.
2. Description of the Related Art
Due to NBTI, the magnitude of the threshold voltage (Vt) of positive-channel metal-oxide semiconductor (PMOS) transistors increases over time which tends to decrease the current flowing through the transistor, for a particular set of bias conditions. A means of detecting the change in Vt and device current is needed. Once the degradation in these two parameters is known, the next step is to compensate for the degradation so that the device performance over the operating life of the product can be maintained.
Currently, there is no active approach (i.e., a circuit implementation) to counteract the effects of NBTI degradation. Today, a special set of reliability device models are used during circuit simulations to understand the effects of device degradation due to NBTI and Hot Carrier Injection (HCI). The result is to over-design the circuit so that it works both at the beginning of life (BOL) as well as at the end of life. This passive approach is challenging because it is difficult to end up with a robust design for all circuits, especially analog circuits, since the process window that must be met is typically larger, making it difficult to consistently design circuits that work over this larger process, voltage, and temperature window.